The invention relates to a blow bar for impactors which, for the purpose of reversibility, has a mirror-symmetrical longitudinal cross-section and features surfaces at the rear as viewed in the rotation direction of the rotor, by means of which the blow bar is supported to the rear and radially from the inside against retaining pieces securely provided on the rotor, and at the front with contact surfaces for movable retaining pieces which hold the blow bar in engagement with the retaining pieces securely provided on the rotor.
Such blow bars which are reversible but not turnable around their longitudinal axis are known in various design forms. They are particularly suited to impactor rotors which comprise a plurality of discs secured on an axle and provided circumferentially with peripheral recesses in which the blow bars are inserted. With such rotors, the inner halves of the blow bar fronts between the discs are also exposed to wear, so that these surfaces cannot be used as support surfaces at the rear. On reversal, i.e. pivoting around a central transverse axis, the rear stays at the rear and the front at the front, only the inner half is then outside and vice versa.
In the vicinity of the disc width, the front support surfaces of the blow bars are adequately protected against wear by the retaining pieces holding them in position or by the leading, more outwardly located rotor disc sections forming the blow bar holder.
Such a blow bar is known, for example, from DE- 26 06 000 A1. Like many other known blow bars, it has a longitudinal cross-section of uniform width; in contrast to other blow bars, however, its cross-section features a rearwardly-angled shape, whereby it is obliquely supported from the inside with the rear surfaces near to the symmetrical axis in contact with appropriately designed rotor disc sections. The blow bar is held in engagement with these parts at the front by wedges which act on the contact surfaces of the blow bar provided centrally at the front vertical and to the symmetrical axis. The contact surfaces for the wedges in the rotor discs at the front are essentially radially aligned.
The cross-section of the known blow bar has a uniform width and thus contingent thereon a wide outer surface area which is essentially exposed to friction wear. A decisive factor for good comminution is the front edge of a blow bar, which should be slightly inclined forward for improved effect. Through such an incline, however, the outer surface area increases further, meaning even more friction wear.
The ideal blow bar would be as thin as possible, as is approximate to that known from DE- 28 11 376 A1. The blow bar described therein is at the most 40 mm thick over a considerable part of its height and hence only suitable for sand impactors where the size of the feed material is relatively small. In addition, this known blow bar is designed for reversible operation, which means that the impact edge is self-whetted by wear. Such a blow bar is unsuitable for large impactors, it would fracture under the load of correspondingly larger feed material.